The invention relates to an apparatus for measuring the mass of a flowing medium, and in particular to measuring the intake air mass of internal combustion engines which includes at least one temperature-dependent resistor arranged in the flow of the medium, the temperature and/or resistance of this temperature-dependent resistor being controlled in dependence on the mass of the flowing medium, and wherein the control variable is a measure for the mass of the flowing medium. The temperature-dependent resistor comprises a hot wire which is mounted to a probe ring mounted in a tubular member through which the medium flows. The temperature-dependent resistor forms part of a bridge circuit which comprises at least one additional temperature-dependent resistor also arranged in the flow of the medium. The bridge circuit is connected to a source of D.C. voltage by way of a multiple contact plug.
An apparatus wherein a hot wire is utilized as the temperature-dependent resistor for measuring the mass of a flowing medium is known. This hot wire is stretched taut in a probe ring at several clamping points and serves as an element of a bridge circuit. The hot wire, and the further elements of the bridge circuit, are connected to contacts of a multiple contact plug, and the multiple contact plug is mounted to a tubular member which defines the flow cross section, the probe ring being arranged within this tubular member.
Certain disadvantages are associated with this known apparatus due to the fact that the contacts become loose, induction tube resistance must be taken into account, and, when used in the intake manifold of an internal combustion engine, interferences, for example from the ignition unit, lead to measuring inaccuracies.